This invention is related to a composite and in particular to a composite structure having an acrylic polymer coating.
Exterior auto and truck parts such as fenders, quarter panels, doors, trim parts bumpers, fender extensions and other molded exterior parts of moldable thermoplastic polymers are currently being used because of their resistance to permanent deformation on impact and their corrosion resistance. Typical moldable thermoplastic polymers that are being use for these parts are polypropylene, polyethylene, ABS (acrylonitrile-butadiene-styrene terpolymers), polystyrene, and styrene-acrylonitrile copolymers. These polymers are easily and economically molded into auto and truck parts that are substantially lighter than currently used sheet metal parts thereby favorably affecting the weight and fuel economy of the auto or truck and are not easily dented or subject to deterioration by corrosion and weathering and are replacing metal parts of automobiles and trucks. Another advantage of these polymers is that more intricate designs can be made in comparison to sheet metals giving the auto makers increased freedom in design of autos.
To reduce air pollution, automobile and truck manufactures need to reduce the amount of painting in the manufacturing process. It would be desirable to have a thermoplastic auto or truck part that has a high quality durable and weatherable surface whose color matches the painted sheet metal used to make the auto or truck and that can attached directly in the assembly process and does not require further priming or painting. This would eliminate the costly and time consuming painting process for thermoplastic parts with the associated pollution problems.
Thermoforming of a thermoplastic sheet having a painted or decorated finish has not been successful with typical exterior acrylic finishes that are used for automobiles and trucks that provide required good appearance with durability and weatherablility. In thermoforming of the thermoplastic sheet to form the part, the finish or decorated surface must flow with the thermoplastic substrate. Typical . automotive thermoplastic acrylic lacquers and thermosetting acrylic enamels are rigid finishes that are impossible to process under thermoforming conditions and crack, distort or degrade. Attempts have been made to reformulate such finishes to flexibilize the finish sufficient for thermoforming but resulted in a finish that is too soft for use as an automotive or truck finish.
It is an objective of this invention to provide a practical and economical process for the preparation of thermoplastic acrylic polymer coated thermoformed parts having an excellent overall appearance and a finish that is durable and weatherable and can be used for the exterior of automobiles and trucks.